This invention relates generally to viscous vortex rate sensors and more particularly to such sensors operating using flueric principles. Specifically, the invention relates to a viscous vortex rate sensor having an adjustable null line or stagnation line for the pickoff located therein. On the pickoff in the flow chamber of a vortex rate sensor there exists some line, which when properly coincident with the stagnation point of the fluid stream within the chamber provides stability to the null signal such that it does not fluctuate with changes in power supply. The power supply is a function of the rate and pressure at which fluid is supplied to the chamber. Thus drift due to fluctuation in the power supply can thus be eliminated by moving the pickoff to achieve the desired result. However, the accuracy required of the mechanisms that would have to be used to manufacture, position, and hold the pickoff at the required orientation in the chamber flow field is at least an order of magnitude greater than the state-of-the-art. Therefore, if the vertical null line of the pickoff can be approximately located near the stagnation point instead of having to be mounted as a detached mechanical member, then, in addition, shifts in position due to mechanical instability will be diminished or eliminated.
The significant factor that inhibits the resolution of the streamline angle of present rate sensors is null shift, a d-c shift of the entire curve of output signal versus angular rate during operation, or a lack of repeatability of the curve when the power supply is shut off and then turned on again. Another factor which inhibits resolution of the streamline angle is signal drift due to low frequency noise. The signal drift is related to variations in the power supply level. The pickoff in the typical sensor is of the push-pull variety and therefore has sensing ports on either side of the stagnation point. Therefore a change in the angle of attack generates pressure changes of opposite signs at the two ports, and a differential signal is then a measure of the angle, or a function of the angular rate.
It is not possible to orient the pickoff so that the differential output is perfectly zero when the sensor is stationary. Thus, the differential signal at zero angular rate is not zero and in particular is dependent upon the flow rate. Hence, variations in flow rate inhibit the measurement of small changes of angular rate above zero rate.
The null shift probably results from flexing or shifting in the pickoff drain assembly caused by the pickoff and drain assembly being mounted in the floor of the sensor chamber as a separate structure.
The invention described herein overcomes all of the disadvantages of the foregoing situation.
It is therefore an object of this invention to provide a new and novel viscous vortex rate sensor which has the capability of adjusting the stagnation point within the sensor chamber precisely to a required vertical null line on the pickoff.
It is another object of this invention to provide a new and novel flueric vortex rate sensor which enables the manufacture of such a sensor with an approximately located pickoff wherein the stagnation point may be adjusted to a null line on the pickoff during operation.
It is yet an additional object of this invention to provide a new and novel flueric vortex rate sensor that increases the resolution of the streamline angle.
It is still an additional object of this invention to provide a new and novel flueric vortex rate sensor which enables the adjustment of the null signal from the pickoff.
Still another object of this invention is to provide a new and novel flueric vortex rate sensor which will eliminate the requirement of a mechanism that can position and hold the pickoff at an orientation in the chamber flow field in order to orient the pickoff at the stagnation point for location of the null signal.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawing which relate to a preferred embodiment of the present invention.